A c. 1936 Workers' Party of Marxist Unification (POUM) poster appeals to workers: "Obreros ¡A la victoria!" ("Workers: to Victory!"). The work was presumably anonymous or collective. The POUM, for whom it was created, was a short-lived organization in 1930s Spain, destroyed in the course of the Spanish Civil War. To the best of my (Joe Mabel's) knowledge, there was no orderly process by which it could assign rights, although the infobox in our article refers (without citation or clarification) to a 1980 dissolution (which would be after the restoration of democracy in Spain). The POUM's legacy has been taken up by the Fundación Andreu Nin, but it is not clear that they hold any legal rights to POUM intellectual property. In any case, under Spanish law, the image is now in the public domain (being anonymous or collective and over 70 years old), but it was in copyright in 1994, thus had its (unregistered) copyright "restored" (really, applied for the first time) in the US, and will apparently remain under U.S. copyright for 90 years from the date of creation. In any case, it barely surpasses the copyrightability of a text logo: the hammer and sickle is certainly not copyrightable, and most of the rest of the poster consists of text and simple shapes.

http://www.fundanin.org/Carteles%20del%20POUM.htm (Fundación Andreu Nin)

POUM

All

Yes, 249 × 360 px for a wall poster

Shows POUM logo; shows graphics typical of their style

Any other comparably relevant replacement would presumably have all the same issues, and possibly introduce additional issues.